Lift-to-weight ratio dependence of lift and stability in an active-Maglev system

In an active-maglev system composed of YBCO bulk and electromagnet, lift-to-weight ratio dependence of lift and stability was investigated experimentally and theoretically. A bulk was levitated by an electromagnet after a field-cooling process for magnetization. It has been shown that lift and stability of the bulk are closely related to both the magnitude of trapped magnetic field and the magnetic field distribution generated by the electromagnet. Minimum field-cooling current for stable levitation, the operating current of electromagnet at initial levitation, and maximum stable-levitation height were measured as a function of the load on the top surface of the bulk. It was observed that the minimum trapped field for stable levitation increased with the load. Maximum permissible displacement in the radial direction was also investigated experimentally as a function of the load and levitation height. The maximum permissible displacement decreases with levitation height and stable-levitation range decreases with weight of load. Numerical analysis based on the three-dimensional finite element method was performed to investigate electromagnetic behaviors within bulk, especially stability at initial levitation. The stability depends on the ratio of operating current at initial levitation to field-cooling current.